The field of the invention is cutting machines, and the invention relates more particularly to devices for trimming hollow objects such as the tops of plastic bottles.
In the production of plastic objects, particularly those made by the process of blow molding, it is often important to make a smooth cut at a hollow opening of the object. Because such objects are often quite thin and deformable, it is often difficult to prepare a smooth cut surface. Often the cutting blade will tend to wander and will produce a somewhat spiral cut. In those instances where the surface must seal against another surface such as a bottle top with a bottle cap, such non-concentric cut can lead to leakage and to rejects. Another common problem is debris if the cut is made by a saw-type cutter.
Numerous approaches have been taken to trim hollow objects. One approach is disclosed in applicant's U.S. Pat. No. 4,445,406 where a dome is molded into the top of a bottle, and the dome is used to support the bottle and rotate it against a knife which is angled into the path of the bottle. While such approach is satisfactory for many applications when a device is particularly thin, or when it is inconvenient for a dome to be molded in the top, such approach is unsatisfactory. An approach utilizing a spinning bottle is shown in U.S. Pat. No. 3,675,521. Another patent showing a method of cutting the top from a bottle while rotating the bottle is shown in U.S. Pat. No. 3,800,638 when the object to be cut is a thin-walled object. The pressure of the knife against the side of the unsupported neck still tends to distort it and occasionally will create a spiralled cut which results in a product which must be discarded as waste.